An accelerator apparatus of an electronic type is known. In this accelerator apparatus, the amount of depression of an accelerator pedal is sensed with a sensor, and the sensor outputs an electrical signal, which indicates the sensed amount of depression of the accelerator pedal, to an electronic control device. For example, the accelerator apparatus of JP2010-158992A includes a pedal rotor and a return rotor. An accelerator pedal is connected to the pedal rotor, and the return rotor is rotatable relative to the pedal rotor. A return spring urges the return rotor in an accelerator closing direction. Furthermore, bevel gear teeth are integrally formed in the pedal rotor such that the bevel gear teeth project toward the return rotor. Also, bevel gear teeth are integrally formed in the return rotor such that the bevel gear teeth project toward the pedal rotor. When the pedal rotor is rotated from an accelerator full-closing position in an accelerator opening direction, the bevel gear teeth of the pedal rotor are engaged with the bevel gear teeth of the return rotor to urge the pedal rotor and the return rotor away from each other.
When the pedal rotor is displaced away from the return rotor, the pedal rotor receives a rotational resistance force through frictional engagement with a first friction member, which is fixed to a support member. When the return rotor is displaced away from the pedal rotor, the return rotor receives a rotational resistance force from a second friction member, which is fixed to the return rotor, by urging the second friction member against the support member. These rotational resistance forces are exerted to maintain the rotation of the accelerator pedal and generate a property of that the pedal force at the time of depressing the accelerator pedal toward a floor is smaller than the pedal force at the time of returning the accelerator pedal away from the floor. This property is referred to as a pedal force hysteresis property. The pedal rotor, the return rotor and the two sets of the bevel gear teeth form a resistance application device, which generates the pedal force hysteresis property.
A value, which is obtained by dividing “a pedal force difference between the pedal force at the time of depressing the accelerator pedal and the pedal force at the time of returning the accelerator pedal” by “the pedal force at the time of depressing the accelerator pedal”, will be referred to as a hysteresis ratio. The inventors of the present application have found that the operability of the accelerator pedal is improved when the hysteresis ratio discussed above is increased from the accelerator-full-closing position of the accelerator pedal (the accelerator-full-closing time) to the accelerator-full-opening position of the accelerator pedal (the accelerator-full-opening time).
In contrast to this finding, in the accelerator apparatus of JP2010-158992A, the urging force, which is exerted by the return spring, is increased or decreased at a constant ratio by the resistance application device and is conducted to the pedal boss. Therefore, the hysteresis ratio is constant throughout a rotational range of the accelerator pedal, which is from the accelerator-full-closing position of the accelerator pedal (the accelerator-full-closing time) to the accelerator-full-opening position of the accelerator pedal (the accelerator-full-opening time), and there is a need for improving the operability of the accelerator pedal.